1. Field of the Invention
The present invention relates to a measuring apparatus which can measure the number and sizes of impurities such as fine dust and bacteria in super-pure water, and more particularly to such a measuring apparatus which determines the number and sizes of the impurities by determining the variation in the electrical resistance between a positive and a negative electrode, the negative electrode being immersed in a sample mixture of the super-pure water and an electrolyte, and the positive electrode being mounted within a hollow sensor which is immersed in the sample mixture, the hollow sensor also containing an electrolyte and having a small hole at its lower end.
2. The Prior Art
A measuring apparatus of the above-noted type which is capable of making measurements of the number and sizes of impurities in separate batches of super-pure water is known. This apparatus includes an open-topped sample container in which the sample batches of super-pure water (containing an electrolyte) are poured; a negative electrode extending into the sample batches; a hollow sensor extending into the sample batches, the hollow sensor having a small hole at its lower end and containing a positive electrode surrounded by electrolyte; means for suitably supplying and removing electrolyte from the hollow sensor; and electrical means connected to the positive and negative electrodes to cause a certain DC to flow therebetween and to detect variations in the resistance (voltage pulses) therebetween which result from impurities passing from the sample batch in the container through the small hole in the hollow sensor. However, because the samples are measured batchwise, they are always exposed to the surrounding atmosphere prior to being measured by the measuring apparatus. As such, these batches will pick up dust and/or bacteria from the surrounding atmosphere, and the subsequent (or contemporaneous) measurement of number and sizes of impurities in the super-pure water will not be representative of the number and sizes of impurities of the super-pure water in its initial condition. This will be less of a problem if the measurements are conducted in a room containing purified air (a "clean room"). However, such clean rooms are very expensive to provide and maintain. In addition, even in a clean room the samples will be exposed to the air therein, and they will thus necessarily contained dissolved nitrogen, which will produce incorrect impurity measurements.